Functional polymers are widely employed as resist materials for high resolution lithography in the manufacture of LSI (Large Scale Integrated Circuits) used in computers.
In recent years, with the growth of LSI manufacturing technology, LSI circuits are achieving even higher densities, and a demand has emerged for resist materials having high resolution and high reproducibility suitable for these densities.
It is theoretically known that an effective way of increasing the resolution of resist materials is to narrow the molecular weight distribution of the polymer used in the resist (monodispersion type polymer).
Conventionally, novolac resins were used as polymers for monodispersion type resist materials, and fractionation was used to control their molecular weight distribution (e.g. Japanese Tokkai Sho 62-121754).
This fractionation operation is however difficult to carry out, requires much time, and does not fully meet stringent performance requirements. A satisfactory solution to this problem was therefore desired.
Chemical amplifier type resist materials having functional groups which can easily be removed by acids and different solubility before and after removal of these functional groups, have been studied due to their excellent workability with a view to improving the manufacturing efficiency of LSI.
Styrene derivative polymers having excellent plasma resistance are examples of such chemical amplifier resist materials.
However, as styrene derivative polymers used as resist materials are conventionally manufactured by radical polymerization or condensation polymerization, it is difficult to control their molecular weight and molecular weight distribution. It was thus difficult to manufacture a styrene derivative polymer of monodispersion type which could fully satisfy the performance requirements of a resist material.
After intensive studies of styrene derivative polymers, the Inventors discovered a novel polymer of the monodispersion type having the performance requirements of a resist material and its method of manufacture, Which led to the present invention.